Electric mine firing device



NQ?. N, SQHMHTT ET AL ELECTRIC MINE FIRING DEVICE Filed oct. 2o. 192s 2 sheets-Smm 1 NOV 37? w33- N. SCHMITT ET AL I L ELECTRIC MINE FIRING DEVICE' Filed Oct. 20. 1928 2 Sheets-Sheet 2 @'51 y E@ i Patented Nov. i7, 1931 UNITED STATES PATENT OFFICE ELECTRIC MINE FIRING DEVICE .Application filed October 20, 1928, Serial No.

The invention relates to electric detonators for tiring blasting charges.

Electric fuses for tiring such charges have previously been proposed comprising an electric conductor so secured in a plug of insulating material arranged in the metal casing or cap of the fuse that a spark for igniting the explosive charge is produced between l the end of the conductor extending into a cavity in the cap and the metallic casing or an intermediate element or material in conductive connection with the latter When the metallic casing and conductor are respectively connected to the respective terminals of a source of alternating current.

Low frequency currents which have hitherto only been employed for operating such fuses have necessitated that at least one of the two conductors must be Very well insulated. This has the disadvantage of making the cost of production relatively high, particularly as the Wires employed for detonators are destroyed in the blasting operation. Moreover when the fuses, as is frequently the case are laid in moist or damp places a further disadvantage is produced by the insulation becoming deteriorated, so that current leakage occurs suiicient to prevent or hinder the operation of the fuse.

lWith a View to obviating these disadvantages a method of firing det-onators according to the invention consists in employlng high frequency alternating current as the ig- -nition current of the order of 50,000-4,000,000 cycles perysecond as employed for example in wireless telegraphy and telephony and produced by any known high frequency generator.`

The invention is based on the knowledge that if a thin Wire connected With a source of high frequency current is brought with its end'remote from that at which the high frequency current is supplied towards another conductor. neither earthed nor connected to the source of current. a spark is produced between the opposed ends ot the conductors so long as the conductor which is being approached has sufficient natural self-capacity. lt is found that high frequency currents "o flowing in a conductor between the source 313,684, and in Germany lvoveaumrY 21, 1927.

of current and detonator are discharged at the end of the conductor extending into the cavity of the detonator not only when the insulation of the conductor is good but also when it is defective, or even (provided the conductor is comparatively short) if it is not insulated at all.

A further advantage obtained by using high frequency ignition currents is that the metal casing of the fuse need not be earthed or connected b y a special conductor with the source of current. Itis only necessary to connect the conductor embedded in the insulating material of the fuse to the one pole of the high frequency current generator, and the use of a second conductor connected to the other pole of the source of current or to ground is unnecessary, thus greatly cheapening andsimplifying the operation. For long distances a metal wire insulated by a thin lacquer coating may be used, whilst for short distances bare conductors may be used.

The value of employing high frequency ignition is still further seen by the fact that a detonator at the end of a bare metal Wire can still be detonated even if the wire is lying in about three feet of water, or if the papercovered wire is secured to trees or walls and the detonator is about 600 yards from the source ofcurrent. there being no need in either case to earth the detonator or connect it by an additional wire to the source of current.

In the accompanying drawings Figure 1 illustrates the principle employed 85 in igniting fuses or detonators according to the. invention. I

Figure 2 is a section through a practical embodiment. 9@

Figures 3 and 4 are, respectively, a sectional and a side elevational view, partly broken away, of a constructional modification.

Tn Fig. 1 the current conducting Wire l of 95 relatively small cross-section terminates below within a suitable priming or detonating pellet 9. The metal member 3 containing the t'uhniuate 5 is in light contact with the pcllet or fusing mass. Upon a high-frequency current being sent into the Wire 1, the mass 2 is fused.

In the embodiment according to Fig. 2 the conducting wire with its priming pellet 20 is surrounded by an insulating substance 4 arranged within the upper portion of the Ymetal shell 6. The lower portion of the latter contains the fulminate 5. For placing the pellet into electrical contact with the shell 6 a metallic connection must be made between the two, which, by way of example, may be in the form of crumpled metal foil 7 (Fig. 2)

` `or loose metal powder, or a metal strap may be inserted contacting with the shell Wall and supporting the pellet. An effective contact is also obtained by providing the insulating substance 4 at its lower portion with a coating 8 of graphite, aluminum or the like metal powder (Figs. 3 and 4) E In experiments which have been carried out a high frequency alternating current of the order of 1,000,000 cycles per second has been employed. The potential of the current emof conducting material is of great moment,

and in the present instance this saving in wire amounts to practically 50%, since only a single conducting wire is required. In addition to the other advantages set forth it may be said that the connecting-up of the shots, o wing to the simplified construction-of the device, can readily be attended to even by an'- unskilled operator.

What I claim is 1. An electric mine fuse for high-frequency operation, comprising a single conducting wire of relatively small cross-section designed for the passage of a high frequency current f and adapted to be connected to one pole of a source of high frequency current, a combus-l tible pellet enclosing the discharge end of the wire in such manner that a spark gap is formed between the extreme point of the wire and the contact point of support of the pellet, a metal shell, a fulminate 1n the closed end portion of the shell, an insulatin member in the open end portion of the shel and a current conductin metal coating on the lower portion of the insulating member.

3. In a detonator for detonating an explo l sive charge by mea-ns of a high frequency current, a metal body, a thin metal conductor insulated from the metal body, said conductor being of restricted cross-sectional dimensions for passage of a high frequency current therethrough and being adapted for connection to a source of high frequency current, a discharge terminal at the end of said conductor and having a cross-section not exceeding the cross section of the conductor, an ignition mass surroundin the discharge terminal, a conductor pow er covering the i nition mass, and a conductive layer of tinse like substance conductivel connecting the said powder and the metal bod NIKOLAUS gCHMITT. OTTO SCHMITT.

wirefin such manner that a .spark gapiisn formed between the extreme point of the wire and the contact point of support ofthe pellet,

i ist a metal shell, a fulminate 1n the bcttomiportion of this shell, and an insulating member in the upper portion thereof, and currentconducting means interposed between, and in contact with, said pellet and said shell and l -forming one terminal of the spark gap for '-coaction with said point of the wire forming `-the other terminal of said gap. A l v 2. Anelectric mine fuse for high-frequency operation, comprising a single lead-in wire 'i of relatively small cross-section, a combusw estiblepellet enclosing the discharge end of the 

